Plasma processing method and plasma processing apparatus

ABSTRACT

In cycle etching in which a depo process and an etching process are repeated, a depo film thickness over a pattern is controlled precisely, and etching is executed to have a desired shape stably for a long time. There are included the depo process (S 1 ) of introducing a reactive gas having a deposit property to a processing chamber and forming a deposit layer over the surface of a pattern to be etched of a substrate to be etched, the etching process (S 2 ) of removing a reaction product of the deposit layer and the surface of the pattern to be etched, and a monitoring process (S 3 ) of irradiating light to the pattern to be etched at the time of the depo process of cycle etching for executing two processes alternately and working a fine pattern and monitoring a change amount of the film thickness of the deposit layer by change of a coherent light having a specific wavelength reflected by the pattern to be etched, the depo process being for forming the deposit layer, in which a processing condition of processes for forming the deposit layer of the next cycle and onward of cycle etching is determined so that an indicator of the depo film thickness calculated from the change amount of the film thickness of the deposit layer monitored falls in a predetermined range compared to reference data.

TECHNICAL FIELD

The present invention relates to a plasma processing method and a plasmaprocessing apparatus, and relates specifically to a technology suitableto plasma etching for controlling the deposition film thickness over apattern.

BACKGROUND ART

Because of miniaturization of the functional element products such as asemiconductor element, development of the device working technology hasbeen accelerated which uses multi-patterning such as double patterningusing the side wall of the spacer of the thin film as a mask.

Accompanying it, in the working process of the device of three-dimensionand the like, the technology of the trench working using variousinsulating material such as a thin film spacer as a mask has becomeimportant. The thickness of the mask, the gate insulation film, the etchstopper, and the like has become thin, and highly selective working ofcontrolling the shape at an atomic layer level has been requested. Also,accompanying implementation of a three-dimensional device, a process forworking a complicated shape has been increasing such as simultaneouslyworking patterns formed in layers with different depth from the wafersurface, and working patterns whose opening dimension changes accordingto the depth. Conventionally, in plasma etching for working Si, an oxidefilm such as SiO₂, and a nitride film such as Si₃N₄, there is known atechnology for etching using a gas mixture having a high depositproperty such as a fluoro-carbon gas and a hydrofluoro-carbon gas inorder to work fine trenches and holes with a high selection ratio withrespect to the material to be etched. In this regard, in PatentLiterature 1, there is disclosed a method for controlling the etchingparameter so that the thickness of the deposition (will be hereinafterreferred to as “depo”) film over a mask becomes within a permissiblevalue during etching.

As the dry etching technology coping with miniaturization, thinning, andhigh selection of the three-dimensional device of recent years,development of the cycle etching technology has been accelerated inwhich working is executed while repeating the depo process of formingthe deposit film by a gas with high deposit property and the etchingprocess of executing etching by ion irradiation and heat and preciselycontrolling the shape. However, in such cycle etching using a gas withhigh deposit property, although it was required to execute etching whileprecisely controlling the depo amount in the depo process and theetching parameter such as the ion energy in the etching process, due tothe temporal change and the like of the state of the etching chamberwall and the atmosphere inside the chamber, it was hard to preciselycontrol the depo process and the etching process stably for a long timeand to execute etching into a desired shape.

On the other hand, as the film thickness measuring technology of a thinfilm, such technology as shown in Non-patent Literature 1 is known whichmeasures the thickness of the adsorption film formed over a flat waferwhere the pattern is not formed and the residual film thickness of thematerial to be etched by ellipsometry in an atomic layer etching inwhich the adsorption process and the desorption process are repeated.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Unexamined Patent Application    Publication No. 2014-232825

Non-Patent Literature

-   Non-patent Literature 1: Journal of Vacuum Science & Technology A32,    020603 (2014)

SUMMARY OF INVENTION Technical Problem

As described above, because of the depo amount and the etching shapeduring the cycle etching work changed by complication andminiaturization of the pattern in the three-dimensional device of recentyears and the temporal change of the atmosphere inside the etchingchamber, it was hard to work a pattern of a desired shape stably for along time. In order to execute working with excellent reproducibility inthe cycle etching, it is required to monitor the depo amount in the depoprocess and the etching amount in the etching process precisely in ashort time and to adjust the etching parameter immediately.

In Patent Literature 1, the deposit film thickness deposited over themask is measured by a film thickness measuring instrument using thecoherent light reflected to the wafer upper surface direction or theabsorption light. In the present prior art, with respect to the filmthickness of the deposit film, a layered structure of depositfilm/mask/SiO₂ is assumed, the absorption factor of each material isobtained beforehand, and the deposit film thickness over the mask ismeasured. However, in this method, when both of the deposit filmthickness over the mask and the film thickness of the mask changed, itwas required to prepare calibration curves beforehand with respect tothe film thickness of plural masks. Also, the film thickness measured bythe present prior art was the deposit film thickness over the mask, thefilm thickness of the deposit film could be measured when etching didnot proceed by blocking of the space portion of the line-and-spacepattern and the opening part of the hole pattern by the deposit filmdeposited excessively over the mask; however, it was hard to measure thedepo film thickness including the side wall of the pattern in thepattern and to obtain information of the working shape. Further, in thecycle etching in which the depo process and the etching process wererepeated in a short time of approximately 0.5 second to several tens ofseconds, it was hard to monitor the depo film thickness and the etchingshape in each cycle on a real-time basis and to control etching.

Next, as described in Non-patent Literature 1, there is known a methodfor achieving etching with the depth accuracy of an atomic layer levelby repeating a process of adsorbing the material to be etched and areaction layer having a reactive property and a process of desorbing areaction product by ion irradiation and the like. In the present priorart, the thickness of the reaction layer and the thickness of thematerial to be etched are measured with the accuracy of an atomic layerlevel by attaching the ellipsometry to the etching chamber. Theellipsometry is known as a method for measuring the film thickness in aflat film by making a polarized incident light enter a sample to bemeasured and measuring the phase difference A of the s-polarized lightand the p-polarized light and the reflection amplitude ratio angle tan ϕof the s-polarized light and the p-polarized light. In this method,because it was required to measure the phase change of the reflectionlight, it was required to acquire many spectra in which polarization waschanged, and it was required to measure the polarization state of thereflected coherent light. Further, in this method, although it isrequired to assume a layered structure of the material to be etched andthe reaction layer and to obtain the refraction index and the extinctionfactor of each material beforehand, because the optical constant of thereaction layer formed during etching changed according to the etchinggas and the etching condition, it was required to obtain the opticalconstant of various reaction layers beforehand. Otherwise, when someoptical constants were unknown, it was required to acquire spectra ofequal to or greater than the number of the unknown number at the lowestand to obtain the unknown number by fitting the simulation resultmodeled on the sample structure, the signal intensity of the coherentlight, and the change of the polarized light. Therefore, in the presentprior art, it was hard to obtain, to monitor on a real-time basis, andto feedback to the etching process the deposit film thickness and thefilm thickness of the material to be etched at every process of cycleetching of alternately executing the depo process and the etchingprocess and working a microscopic pattern. Furthermore, although thefilm thickness could be obtained precisely with respect to the layeredfilm whose optical constant was known, it was hard to calculate the depofilm over the pattern and the working shape of the pattern to be etched.

The object of the present invention is to provide a plasma processingmethod and a plasma processing apparatus in which, in cycle etching, thedepo film thickness formed in the depo process or the working shapeformed in the etching process is monitored, and the depo film thicknessor the working shape is controlled on a real-time basis.

Solution to Problem

In order to achieve the object described above, in the presentinvention, there is provided a plasma processing method for etching afilm to be etched by repeating a depositing process for forming adeposit layer over the film to be etched and a removing process forremoving a reaction product of the deposit layer and the film to beetched, including a monitoring process for monitoring a change amount ofa film thickness of the deposit layer using change of a coherent lightthat is obtained by irradiating a polarized light polarized to apredetermined angle with respect to a mask pattern of the film to beetched and is reflected by the mask pattern.

Also, in order to achieve the object described above, in the presentinvention, there is provided a plasma processing apparatus including aprocessing chamber where a sample is plasma-processed, a film to beetched being formed over the sample, a radio frequency power source thatsupplies radio frequency power for generating plasma, a sample deck onwhich the sample is mounted, a light source that irradiates light, apolarization filter that polarizes light irradiated from the lightsource to a predetermined angle with respect to a mask pattern of thefilm to be etched, a rotation mechanism that controls the rotation angleof the polarization filter, and a control unit where a change amount ofa film thickness of a deposit layer over the film to be etched isobtained using change of a coherent light that is obtained byirradiating the light polarized by the polarization filter whoserotation angle is controlled by the rotation mechanism and is reflectedby the mask pattern.

Advantageous Effects of Invention

According to the present invention, it is enabled to control the etchingprocess on a real-time basis, and a fine pattern can be stably workedhighly precisely with excellent reproducibility without a fluctuation inthe process.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing that shows an example of a process flow of anetching method of the first embodiment.

FIGS. 2(a) and 2(b) are schematic drawings for explaining a process flowof an etching method of the first embodiment.

FIG. 3 is a schematic drawing that shows the relation between thepolarization direction of the monitoring light and the line direction ofthe pattern to be etched related to the first embodiment.

FIG. 4 is a drawing that shows an overall configuration example of anetching apparatus that is a plasma processing apparatus related to thefirst embodiment.

FIGS. 5(a) and 5(b) are explanatory drawings of the notch direction ofthe wafer of the apparatus, the line-and-space pattern, and the rotationdirection of the polarization filter related to the first embodiment.

FIGS. 6(a) to 6(c) illustrate examples of the temporal change of theindicator of the depo film thickness and the indicator of the etchingamount of the reference data related to the first embodiment.

FIGS. 7(a) to 7(f) are schematic drawings for explaining the indicatorof the etching amount of the first embodiment.

FIGS. 8(a) and 8(b) show a calculation method for the indicator of thedepo film thickness of the first embodiment and an example of themonitoring result thereof.

FIG. 9 is an explanatory drawing of an example of the adjusting methodof the depo process time of the first embodiment.

FIG. 10 is an explanatory drawing of an example of the polarizationdirection of light of a case where the pattern to be etched of the firstembodiment is a hole pattern.

FIG. 11 is a drawing that shows an example of an overall configurationof the cluster type etching tool related to the second embodiment.

DESCRIPTION OF EMBODIMENTS

Below, embodiments of the present invention will be explained in detailusing the drawings. Also, in all drawings, those having a same functionare marked with a same reference sign, and repeated explanation thereofwill be omitted.

The etching method of the present invention is a plasma processingmethod for etching a film to be etched by repeating a depositing processfor forming a deposit layer over the film to be etched and a removingprocess for removing a reaction product of the deposit layer and thefilm to be etched, and further includes a monitoring process formonitoring a change amount of a film thickness of the deposit layerusing change of a coherent light that is obtained by irradiating apolarized light polarized to a predetermined angle with respect to amask pattern of the film to be etched and is reflected by the maskpattern. Thereby, the working condition of the pattern to be etched ofthe next cycle is adjusted on a real-time basis, and the substrate to beetched is precisely worked stably for a long time.

Also, the plasma processing apparatus of the present invention includesa processing chamber where a sample is plasma-processed, a film to beetched being formed over the sample, a radio frequency power source thatsupplies radio frequency power for generating plasma, a sample deck onwhich the sample is mounted, a light source that irradiates light, apolarization filter that polarizes light irradiated from the lightsource to a predetermined angle with respect to a mask pattern of thefilm to be etched, a rotation mechanism that controls the rotation angleof the polarization filter, and a control unit where a change amount ofa change amount of a film thickness of a deposit layer over the film tobe etched is obtained using change of a coherent light that is obtainedby irradiating the light polarized by the polarization filter whoserotation angle is controlled by the rotation mechanism and is reflectedby the mask pattern.

As described above, in the embodiments of the present invention, themonitor unit includes the rotation mechanism that rotates thepolarization filter so that at least a part of a measuring area becomesan orthogonal direction to the line direction of the line-shape patternto be etched and to make the polarized light incident, the measuringarea being obtained by extracting the regularity of the pattern of thelayout information of the pattern to be etched. Further, the controlunit acquires the temporal change of the coherent light of pluralwavelength from the reference pattern in the middle of working a desiredshape as the reference data beforehand, extracts the signal intensity ofthe coherent light with a specific wavelength where the intensitydifference with the coherent light of the real time in the depo processand the etching process becomes a constant value or more, calculates thefitting curve from the signal intensity of the coherent light at thetime of finishing the etching process, calculates the indicator of thedepo film thickness from the difference between the fitting curve andthe signal intensity at the time of finishing the depo process, orcalculates the indicator of the etching amount from the inclination ofthe fitting curve. When the indicator of the calculated depo filmthickness or the indicator of the etching amount goes out of thepredetermined range determined based on the reference data that is onthe basis of the reference pattern stored in the database, theprocessing condition in the depo process or the etching process of thecycle of the next time and onward is determined.

First Embodiment

As the first embodiment, an embodiment of the cycle etching and theetching apparatus in which the depo process and the etching process areexecuted alternately and a fine pattern is worked will be explained.FIG. 1 is a drawing that shows an example of a process flow of the cycleetching including plural steps (S) related to the first embodiment.FIGS. 2(a) and 2(b) are schematic drawings for explaining the processflow of FIG. 1, FIG. 2(b) is an explanatory drawing of the depo process(S1) and (b) is an explanatory drawing of the etching process (S2). Inthe present embodiment, as an example of the pattern to be etched,explanation will be made for the case of etching a material to be etched2 when inter-layer films of a non-etching layer 4 and the material to beetched 2 are formed over a wafer 1 as a substrate to be etched, and afine line-and-space pattern that is the pattern to be etched is formedin a mask 3. Also, in the present embodiment, although explanation willbe made for the case where etching is executed using energy of ions inS2, etching may be executed using other energy supply means such as heatprocessing.

When the process flow of FIG. 1 is started, as shown in FIG. 2(a), adepo film 5 is formed over the wafer 1 that includes the material to beetched 2 and is formed with a pattern by the mask 3 (S1). Next, ionsformed by the plasma and the like are irradiated to the pattern to beetched. As shown in FIG. 2(b), at the surface of the material to beetched 2 out of the pattern to be etched, the depo film 5 and thematerial to be etched 2 react with each other by energy supplied fromthe ions, and etching proceeds (S2). On the surface to be etched of themask 3, side walls 6, and the like, energy of the ions is lost by thedepo film 5, and etching of the surface to be etched is suppressed. Inthe present embodiment, although the case of executing etching usingenergy of the ions in S2 is shown, as described above, etching may beexecuted using other energy supply means such as heat processing.According to the cycle etching method, formation of the depo film 5 (S1)and the etching process (S2) are made 1 cycle, and, by repeating thiscycle by required number of times, the material to be etched 2 is etchedto a predetermined depth.

According to the cycle etching method described above, the thickness ofthe depo film deposited in the depo process of one time is as thin asseveral atomic layers-several tens of nm, the etching depth etched inthe etching process of one time is also as thin as several atomiclayers-several tens of nm, and it is required to precisely control thedepo film thickness and the etching amount in each process. However, thedepo amount of the pattern surface is largely affected by the atmosphereinside the chamber, and, in the production site of the device, it hasbecome a problem that the atmosphere inside the chamber changes by thedeposited object and the like adhered to the etching chamber wall whilea large amount of the wafers is processed and a desired working shape isnot obtained.

Therefore, as shown in S3 and S4 of the process flow of FIG. 1, in thecycle etching of the present embodiment, the indicator of the filmthickness of the depo film 5 deposited over the surface of the patternto be etched and the indicator of the etching amount are monitored, andthe processing condition of the depo process or the etching process isadjusted on a real-time basis. That is to say, in forming the depositlayer by the cycle etching, light polarized to a predetermined angle isirradiated to the pattern to be etched, the change amount of the filmthickness of the deposit layer is monitored by change of the coherentlight having a specific wavelength reflected by the pattern to beetched, the indicator of the film thickness of the depo film and theindicator of the etching amount are obtained, and the processingcondition is adjusted on a real-time basis using these indicators.

FIG. 3 is a schematic drawing that shows the relation between thepolarization direction of the incident light for monitoring the depofilm thickness in the present embodiment and the line direction of theline-and-space pattern that is the pattern to be etched. In the presentembodiment, because the depo film thickness formed over the pattern ismonitored in the depo process (S1), a line direction 9 of theline-and-space pattern is extracted as information showing theregularity of a line-and-space pattern 7 formed beforehand over the maskfrom the layout information of the pattern to be etched, a polarizationfilter 8 is rotated so as to become the orthogonal direction to a linedirection 9 based on the information of the line direction 9 extracted,and the polarized light is made incident. Also, based on the temporalchange of the signal intensity of the coherent light having a specificwavelength reflected on the wafer, the change amount of the filmthickness of the deposit layer is monitored on a real-time basis, andthe indicator of the depo film thickness and the indicator of theetching amount are calculated.

For example, in such relation showing an example in FIG. 3, when theline direction 9 is X-direction, the direction of the polarizationfilter 8 is adjusted by rotating the polarization filter 8 toY-direction. Thus, when light is made incident on the line-and-spacepattern to such direction that the line direction 9 of theline-and-space pattern and a polarization direction 10 by thepolarization filter 8 become orthogonal (90 degrees), the coherent lightreflected causes a diffractive effect by the line-and-space pattern andchanges sensitively responding a change of the cross-sectional shape ofthe line-and-space pattern, therefore the indicator of the filmthickness of the depo film and the indicator of the etching amount canbe calculated, and a change of the depo film thickness in the deposprocess and the etching shape in the etching process come to be capableof being precisely monitor-controlled using these indicators.

In FIG. 4, an overall configuration of an etching apparatus forachieving the cycle etching method of the present embodiment is shown.An etching apparatus 20 that is a plasma processing apparatus isconfigured of a processing chamber 21, a gas supply unit 23, a monitorunit 28, a monitor control unit 29, an apparatus control unit 36, and soon. The monitor control unit 29 including a control unit 108, acalculation unit 109, and a database 110 and the apparatus control unit36 including plural mechanism blocks are achieved by execution of aprogram of a computer including a central processing unit (CPU), astorage unit, and the like respectively, and the both are connected toeach other by a control line 47. Also, the apparatus control unit 36functions as a function block of a gas control unit 37, an exhaustsystem control unit 38, a radio frequency control unit 39, a biascontrol unit 40, a storage unit 41, a clock 42, and so on. Thesefunction blocks can be achieved by one set of the personal computer (PC)as described above. Further, in the present description, there is a casewhere the monitor control unit 29 and the apparatus control unit 36 arecollectively referred to simply as a control unit.

In the etching apparatus 20, a wafer stage 22 arranged inside theprocessing chamber 21 and the gas supply unit 23 including gas cylindersand valves are arranged, each of a depo process gas 24 and an etchingprocess gas 25 is supplied to the processing chamber 21 in the processstep shown in FIG. 1 based on a control signal 46 from the apparatuscontrol unit 36. The process gas supplied is decomposed to plasma in theinside of the processing chamber 21 by radio frequency power 44generated by a radio frequency power source 27 and applied to a radiofrequency application unit 31. Also, the pressure inside the processingchamber 21 can be kept constant by a variable conductance valve and avacuum pump in a state the process gas of a desired flow rate is made toflow, the variable conductance valve and the vacuum pump being connectedto the processing chamber 21, illustration of the variable conductancevalve and the vacuum pump being omitted.

First, when the depo process (S1) starts, the depo process gas 24 issupplied to the processing chamber 21 at a predetermined flow rate basedon the control signal 46. The depo process gas 24 supplied becomesplasma by the radio frequency power 44 applied to the radio frequencyapplication unit 31, and is decomposed into radicals, ions, and thelike. The radicals and the ions formed by the plasma reach the surfaceof the wafer 1, and form the depo film 5 shown in FIG. 2(a). Next, whenthe etching process (S2) starts, the etching process gas 25 is suppliedto the processing chamber 21 at a predetermined flow rate. The gas 25supplied becomes plasma by the radio frequency power 44 applied by theradio frequency application unit 31, is decomposed into radicals andions, and is irradiated to the surface of the wafer 1. At this time,when etching is executed by the ions irradiated from the plasma, it ispossible to apply a bias voltage 45 supplied from a bias power source 30to the wafer stage 22 for example and to control ion energy.

The kind of the gas used in each process is selected appropriatelyaccording to the pattern material for which the etching process isexecuted. For example, as the depo process gas 24, a gas mixture of afluorocarbon gas and a hydrofluorocarbon gas such as C₄F₈ and CH₃F, arare gas, and O₂-, CO₂-, N₂-gas and the like can be used. At this time,as the etching gas, for example, a gas mixture of a fluorocarbon gas anda gas such as Ar, He, Ne, Kr, and Xe, and O₂, CO₂, CF₄, N₂, H₂,anhydrous HF, CH₄, CHF₃, NF₃, SF₃, and the like can be used. Also, forexample, when a gas mixture of HBr, BCl₃ and the like, a rare gas, andCl₂-, O₂-, CO₂-, and N₂-gas and the like is used as the depo process gas24, as the etching gas 25, a gas mixture of HBr, BCl₃, and the like, arare gas such as Ar, He, Ne, Kr, and Xe, and Cl₂, O₂, CO₂, CF₄, N₂, H₂,anhydrous HF, CH₄, CHF₃, NF₃, SF₃, and the like can be used for example.

Next, one concrete example of a method for monitoring the indicator ofthe depo film thickness and the indicator of the etching amount duringthe cycle etching process by the monitor unit 28 and the monitor controlunit 29 in the configuration of the etching apparatus of the presentembodiment will be explained. FIGS. 5(a) and 5(b) are drawings forexplaining the relation of the notch direction of the wafer 1, the linedirection 9 of the line-and-space 7, and the rotation direction of thepolarization filter 8. First, the wafer 1 where the reference pattern ofa desired shape is patterned as the reference data is introduced to theprocessing chamber 21. As shown in FIG. 5(b) of the drawing, thedirection of a notch 11 or the direction of the orientation flat of thewafer introduced to the processing chamber is disposed in a directionhaving been set beforehand. The relation between the direction of thenotch 11 or the orientation flat of the wafer and the line direction 9of the reference pattern is stored beforehand as the wafer informationin the database 110 of the monitor control unit 29, the storage unit 41of the apparatus control unit 36, and so on.

In the monitor unit 28, light generated from a monitor light source 102is polarized by the polarization filter 8 whose rotation is controlledby a rotation mechanism 103, and is irradiated on the reference patternover the wafer 1. At this time, as the monitor light source 102, lightwith the wavelength range of 190 nm to 900 nm for example is used. Thepolarization filter 9 rotates using the rotation mechanism 103 and canadjust the polarization direction 10 based on control of the monitorcontrol unit 29 according to the information of the line direction 9 ofthe line-and-space pattern 7 of the wafer. Here, the polarizationdirection 10 of an incident light 104 after passing through thepolarization filter 8 is adjusted to be orthogonal to the line direction9 of the line-and-space pattern 7 of the reference pattern according tothe wafer information stored in the storage unit 41 of the apparatuscontrol unit 36.

Then, at the same time etching is started, monitoring of the referencepattern over the wafer 1 is started. The light generated from themonitor light source 102 is polarized by the polarization filter 8 andis irradiated on the reference pattern over the wafer 1. Because theline direction 9 of the line-and-space pattern 7 formed over the wafer 1is normally X-direction or Y-direction with respect to the notch of thewafer, the polarization direction 10 of the polarization filter 8 may beadjusted beforehand to X-direction or Y-direction according to theinformation of the wafer 1. Next, a coherent light 105 reflected by thereference pattern passes through a detection unit 26 and an opticalfiber 106 of the monitor unit 28, and is dispersed by a spectralapparatus 107. At this time, with respect to the coherent lightdispersed by the spectral apparatus 107, by being made to pass throughagain the polarization filter 8 that has polarized the incident light104, only the light polarized in one direction may be detected. In thespectral apparatus 107 of the monitor unit 28, the temporal change ofthe signal intensity of the coherent light having predetermined pluralwavelengths is measured. The indicator of the depo film thickness andthe indicator of the etching amount at the reference pattern arecalculated by the calculation unit 109 of the monitor control unit 29from the temporal change of the signal intensity of the coherent lighthaving at least one specific wavelength having been measured.

In FIG. 6(a), there is shown an example of the temporal change of thesignal intensity (I) having a specific wavelength of the coherent lightacquired as the reference data using the reference pattern using theconfiguration of the present embodiment. In the case of the presentexample, when etching is started, the signal intensity increases in thedepo process (S1), and the signal intensity reduces in the etchingprocess (S2). In the present embodiment, based on the temporal change ofthe signal intensity (I) of a specific wavelength of the coherent lightacquired as this reference data, the thickness and the etching shape ofthe depo film 5 are controlled and the pattern of a desired shape isstably formed in S3 and S4 of the cycle etching method of FIG. 1.Therefore, the monitor control unit 29 acquires beforehand the temporalchange of the coherent light having plural wavelengths in the middle ofworking the desired shape as the reference data, and extracts the signalintensity of the coherent light having a specific wavelength where thesignal intensity difference of the coherent light in the depo process(S1) and the etching process (S2) becomes maximum for example.

Here, one concrete example of the calculation method for the indicatorof the depo film thickness and the indicator of the etching amount usedin determination of S3 and S4 of the process flow by the calculationunit 109 will be explained. Also, each indicator calculated is stored inthe database 110 as the reference data. That is to say, by storing asthe reference data the indicator of the depo film thickness and theindicator of the etching amount calculated based on the change of thecoherent light of this specific wavelength reflected by the referencepattern of the pattern to be etched and comparing the indicator of thedepo film thickness or the indicator of the etching amount calculatedfrom the change amount of the film thickness of the deposit layermonitored and these stored reference data, the processing condition ofthe next cycle and onward can be determined.

As shown in FIG. 6(a), in an example of the signal intensity (I) of thecoherent light from the reference pattern, first, the signal intensityincreases in the depo process and the signal intensity reduces in theetching process. When etching proceeds further, the signal intensityreduces in the depo process and the signal intensity increases in theetching process. Also, we found out that a fitting curve 111 of thesignal intensity of the coherent light having a specific wavelength atthe time of completion of the etching process changed depending on theinformation of the working shape of the pattern to be etched aftercompletion of the etching process and that the difference of thisfitting curve 111 and the signal intensity after completion of the depoprocess depended on the thickness of the depo film formed in the depoprocess.

Further, as a result of monitoring an absolute value |d/a₀| of a valueobtained by standardizing the difference d between the signal intensityat the time of completion of the etching process of the (n−1)-th cycleand the signal intensity at the time of completion of the depo processof the n-th cycle by the inclination a₀ of the fitting curve as anindicator r of the depo film thickness as shown in FIG. 6(b) as anexample of the indicator r of the depo film thickness, the relationbetween the change of the indicator of the depo film thickness and thecross-sectional shape after etching was found out. The reference data inthe drawing shows the temporal change of the indicator of the depo filmthickness calculated based on the reference pattern. Based on thisrelation, the indicator of the depo film thickness can be calculatedfrom the difference between the signal intensity of the coherent lighthaving a specific wavelength at the time of completion of the etchingprocess and the signal intensity of the coherent light having thespecific wavelength at the time of completion of the depo process tofollow. Thereby, in the monitoring process, based on the differencebetween the signal intensity of the coherent light of the etchingprocess and the signal intensity of the coherent light of the depoprocess, the change amount of the film thickness of the deposit layercan be monitored.

Also, as shown in FIG. 6(c), it was found out that, when the amplitudeand the cycle length which are the shape of the fitting curve 111 of thesignal intensity at the time of completion of the etching process or, inother words, the signal intensity (amplitude) of the fitting curve orthe cycle length of the fitting curve at a predetermined time shiftedfrom a desired shape of the fitting curve based on the referencepattern, the shape of the fitting curve changed according to thecross-sectional shape. As a result, the indicator of the etching amountcan be calculated based on the amplitude and the cycle length of thefitting curve of the signal intensity of the coherent light having aspecific wavelength.

FIGS. 7(a) to 7(f) are explanatory drawings for an example of variouscross-sectional shape of a pattern to be etched, and Table 1 is a tablethat shows an example of the category of the cross-sectional shape ofthe etching pattern determined from the indicator of the depo filmthickness and the indicator of the etching amount, the adjustment methodfor the processing parameter of the depo process, and the adjustmentmethod for the processing parameter of the etching process.

TABLE 1 Category Indicator determination Adjustment Adjustment ofIndicator of of of depo of etching depo film etching cross-sectionalprocess process thickness amount shape parameter parameter r > r₀₁ Cyclelength Etch stop Reduction of Increase of S > S₁ ≈ ∞ time or small timeor Amplitude I < flow rate increase of I₁ ≈ 0 ratio of bias voltagesedimentary or increase gas/entire of bias gas voltage on/off time ratior > r₀₂ Amplitude I < Taper Reduction of Increase of I₂ time or smalltime or flow rate increase of ratio of bias voltage sedimentary orincrease gas/entire of bias gas voltage on/off time ratio r > r₀₃ Cyclelength Line width Reduction of Increase of S > S₃ increases time orsmall time or flow rate increase of ratio of bias voltage sedimentary orincrease gas/entire of bias gas voltage on/off time ratio r > r₀₄ Cyclelength Line width Increase of Reduction of S < S₄ reduces time or largetime or flow rate drop of bias ratio of voltage or sedimentary drop ofbias gas/entire voltage gas on/off time ratio r > r₀₅ Amplitude I <Bowing Increase of Reduction of I₅ time or large time or drop flow rateof bias ratio of voltage or sedimentary drop of gas/entire bias voltagegas on/off time ratio

For example, when the cross-sectional shape of the reference pattern isa perpendicular pattern shown in FIG. 7(a) and when the indicator of thedepo film thickness is larger than a designated permissible range r₀₁and the change of the indicator of the etching amount is less than adesignated value I₁, the cross-sectional shape of the actual etchingpattern can be determined to be the etch stop of FIG. 7(b) for example.Also, when the indicator of the depo film thickness is larger than adesignated permissible range r₀₂ and the change of the indicator of theetching amount namely the change of the amplitude is less than adesignated value I₂ for example, the cross-sectional shape can bedetermined to be the tapered shape of FIG. 7(c) for example. In asimilar manner, when the indicator of the depo film thickness is largerthan a designated permissible range r₀₃ and the change of the indicatorof the etching amount namely the change of the cycle length is largerthan a designated value S₃ for example, the cross-sectional shape can bedetermined for example to be a cross-sectional shape where the linewidth of FIG. 7(d) increases, and when the indicator of the depo filmthickness is less than a designated permissible range r₀₄ and the changeof the indicator of the etching amount namely the change of the cyclelength is less than a designated value S₄ for example, thecross-sectional shape can be determined for example to be across-sectional shape where the line width of FIG. 7(e) reduces. Also,when the indicator of the depo film thickness is less than a designatedpermissible range r₀₅ and the change of the indicator of the etchingamount namely the change of the amplitude is less than a designatedvalue I₅ for example, the cross-sectional shape can be determined forexample to be a bowing cross-sectional shape of FIG. 7(f).

Therefore, in the etching apparatus 20 of the present embodiment, thecoherent light spectrum, the indicator of the depo film thickness, andthe indicator of the etching amount of the reference pattern accumulatedin the database 110 and the coherent light spectrum, the indicator ofthe depo film thickness, and the indicator of the etching amount whichare the actual monitoring results are compared to each other by themonitor control unit 29. This comparison is executed by the calculationunit 109 of the monitor control unit 29. When the comparison resultdeviates from the specific range shown by the permissible range of FIG.6 for example, the control unit 108 adjusts/determines the processingcondition of the depo process (S1) and the etching process (S2) of thecycles of the next time and onward, and controls so that the processingcondition after being adjusted/determined is transmitted to theapparatus control unit 36.

Next, a case of monitoring the change amount of the film thickness ofthe deposit layer, monitoring the indicator of the depo film thicknessand the indicator of the etching amount of the pattern to be etched, andcontrolling etching on a real-time basis by the etching apparatus of thepresent embodiment shown in FIG. 4 will be explained. First, the wafer 1where a pattern similar to the reference pattern is patterned as a waferto be etched is introduced to the processing chamber 21, the referencepattern being measured beforehand, the reference data being stored inthe reference pattern. At this time, the notch 11 or the orientationflat of the wafer 1 is disposed at a position set beforehand. Therelation between the direction of the notch 11 or the orientation flatof the wafer and the line direction 7 of the reference pattern is storedbeforehand in the storage unit 41 of the apparatus control unit 36 asthe wafer information. With respect to the polarization filter 8,similarly to the time when the reference pattern was monitored, therotation angle of the polarization filter 8 is adjusted by the rotationmechanism 103 by control of the monitor control unit 29 so as to becomeorthogonal to the line-and-space pattern 7 of the pattern to be etchedaccording to the wafer information of the wafer that is a substrate tobe etched stored in the storage unit 41.

At the same time etching of the wafer to be etched is started,monitoring of the pattern to be etched by the monitor unit 28 isstarted. Similarly to the case of acquiring the reference data before,the incident light 104 generated from the monitoring light source 102 ofthe monitor unit 28 is polarized by the polarization filter 8, and isirradiated on the pattern to be etched over the wafer 1. Next, similarlyto the case of acquiring the reference data, the coherent light 105reflected by the wafer 1 passes through the detection unit 26 and theoptical fiber 106, and is measured by the spectral apparatus 107. In thespectral apparatus 107, the temporal change of the signal intensity ofthe coherent light having a specific wavelength determined when thereference data were acquired beforehand is monitored. From the temporalchange of the coherent light having the specific wavelength monitored bythe monitor unit 28, the calculation unit 109 calculates the indicatorof the depo film thickness and the indicator of the etching amountsimilarly to the reference data before.

In FIGS. 8(a) and 8(b), there is shown an example of a case, when theindicator of the depo film thickness becomes a value deviating from aspecific range, the process condition of the depo process is adjustednamely the indicator of the depo film thickness of the pattern to beetched is monitored, the time of the depo process is adjusted on areal-time basis, and etching is executed while being controlled to havea desired etching shape. FIG. 8(a) shows an example of the temporalchange of the signal intensity (I) of the coherent light having aspecific wavelength similarly to FIG. 6(a), and an example of thetemporal change of the indicator r of the depo film thickness is shownin FIG. 8(b). For example, when the indicator r (n) of the depo film ofthe n-th cycle is small exceeding the permissible range of r(n), thedepo time t(n+1) of the depo process of the (n+1)-th cycle is determinedfor example by the control unit 108 as follows.

In FIG. 9, as an example of the adjusting method for the depo time ofthe depo process, there is shown the temporal change of the indicator rof the depo film thickness within the depo process of the n-th cycle ofthe reference data. When a value required as the indicator of the depofilm thickness of the (n+1)-th time is made r₀(n+1), the difference ofr₀(n+1) and r(n) is made Ar, the processing time of the depo process ofthe n-th time is made t, and the inclination of the indicator of thedepo film thickness at the time t is made b, the processing time of the(n+1)-th time t(n+1) can be determined as (Ar/b+t(n)). Thus, when thetime of the depo process of the (n+1)-th time was adjusted, theindicator r(n+1) of the depo film thickness of the (n+1)-th time couldbe controlled to within the permissible range of the indicator of thedepo film of the (n+1)-th time. Further, also in the case where theindicator r(m) of the depo film became large in the m-th time exceedingthe predetermined range illustrated as the permissible range as shown inFIG. 8(b), the depo film thickness could be controlled to within adesired range by adjusting the processing time of the depo process ofthe (m+1)-th time from the measured value of the temporal change of theindicator of the depo film thickness within the depo process of the m-thtime. Because of the configuration of the present embodiment, byadjusting the depo time so that the indicator of the depo film thicknessbecame within the predetermined range in each cycle, it was enabled tocontrol the etching shape to execute etching for a long time withexcellent reproducibility.

Thus, when the indicator of the depo film thickness has been determinedto deviate from the predetermined range, as the processing parameter tobe adjusted other than the time of the depo process, as shown in ice,there is the mixing ratio of the etching gas and the like for example,and a means for adjusting it can be arranged. For example, when theratio of the sedimentary gas and the entire gas flow rate is to beadjusted as the mixing ratio of the etching gas, a data file that hasacquired beforehand the relation against the change amount of theindicator of the depo film thickness of the case where the flow rateratio of the etching gas is changed is kept in the storage unit 41, aportion of the difference Ar of the indicator r of the depo filmthickness measured and the predetermined value r₀ is changed, and thegas flow rate ratio that allows the indicator of the depo film thicknessto fall in the predetermined range is calculated by the calculation unit109. The gas flow rate ratio calculated was transferred to the gascontrol unit 37, and it was enabled to control the gas flow rate ratio.

On the other hand, when the indicator of the etching amount wasdetermined to deviate from the predetermined range in spite that theindicator of the depo film thickness was within the predetermined range,by a means for adjusting the time of the etching process, the wafer biasvoltage, and the wafer temperature for example, it was enabled toprecisely control the etching shape. For example, when the wafer biasvoltage of the etching process is to be adjusted by the bias controlunit 40, the wafer bias voltage can be fine-adjusted so that theindicator of the etching amount falls in the predetermined range asshown in the column of adjustment of the etching process parameter ofTable 1. The adjustment value of the wafer bias voltage 45 calculated bythe calculation unit 109 is transferred to the bias control unit 40, andthe bias power source 30 can be adjusted to a predetermined value. In asimilar manner, fine adjustment can be executed by increasing/decreasingthe time of the etching process using the radio frequency control unit39 and the like.

In the present embodiment described above in detail, a case where thepattern to be etched was a line-and-space pattern was explained forexample. However, the configuration of the present embodiment is notnecessarily implemented so as to be limited only to a line-and-spacepattern. For example, as shown in FIG. 10, the configuration of thepresent embodiment can be implemented also to a case where the patternto be etched is a hole pattern. An explanatory drawing for an example ofa method for setting the polarization direction of the incident light ofthis case is shown. As shown in FIG. 10, when the pitch of a holepattern 120 is different between x-direction and Y-direction, namelywhen the pitch of one direction in the hole pattern is smaller than thepitch of the other direction in the hole pattern, the incident light ispolarized orthogonal to the pitch of one direction, and monitors thechange amount of the film thickness related to the deposit layer of theside wall of the hole pattern on the side of the other direction. Forexample, by adjusting rotation of the polarization filter 8 so that thedirection along which the pitch is small namely X-direction becomesorthogonal to the polarization direction 10 of the incident light 104,the indicator of the depo film thickness and the indicator of theetching amount with respect to a side wall 121 with a larger pitch canbe precisely monitored.

However, when a fine pattern is to be worked, there is also a case whereit is necessary to control a side wall shape 122 in the direction with asmaller pitch more precisely. In such case, highly precise monitoringbecame possible by adjusting the rotation angle of the polarizationfilter 8 so that the direction with a larger pattern pitch namelyY-direction became orthogonal to the polarization direction 10 of theincident light 104. Moreover, it is also possible to monitor the depofilm and the etching shape of the hole with high sensitivity by rotatingthe polarization filter 8 to X-direction and Y-direction alternately ata high speed by the rotation mechanism 103 and alternately measuring thesignal intensity of the coherent light in irradiating the incident lightpolarized to X-direction and the signal intensity of the coherent lightin irradiating the incident light polarized to Y-direction.

By the configuration of the present embodiment, it is enabled tocalculate the indicator of the depo film thickness or the indicator ofthe etching amount from the change amount of the film thickness of thedeposit layer monitored by the monitor unit, to determine the processingcondition of the depo process or the etching process of the next cycleand onward of the cycle etching based on the indicator of the depo filmthickness or the indicator of the etching amount having been calculated,and to process the substrate to be etched with the determined processingcondition.

Second Embodiment

Next, a plasma processing apparatus configured of a cluster type etchingtool (will be hereinafter referred to as a cluster tool) of the secondembodiment will be explained using FIG. 11. FIG. 11 is a drawing thatshows a configuration of the cluster tool of the second embodiment. Asan example of the present cluster tool, a case of configuring theprocessing chamber of the etching apparatus by three chambers will beshown. In addition to three processing chambers, the cluster toolincludes a wafer cassette loader 204, a control PC 205, a convey robot207, a control unit 220, and a notch position adjustment stage 221. Inthe configuration of the present embodiment, the control PC, the controlunit 220, and the three monitor control units 36 can be collectivelyreferred to as a control unit of the cluster tool.

In the present cluster tool, when the wafer cassette is set to the waferloader 204, based on the process recipe having been set beforehand bythe control PC 205, the wafer 1 for processing is conveyed from thewafer cassette onto a rotation deck 206 of the notch position adjustmentstage 221 for notch position alignment by the convey robot 207. In therotation deck 206, the direction of the notch 11 is aligned to apredetermined direction 208 under control of the control unit 220according to information of the processing chamber in which the notchposition of the wafer 1 for processing is designated by the processingrecipe. When alignment of the notch has been completed, the wafer 1 forprocessing is conveyed from the rotation deck 206 to a load lock chamber212 by the convey robot 207.

When the wafer 1 is conveyed to the load lock chamber 212, the load lockchamber 212 is pumped to a predetermined degree of vacuum. When the loadlock chamber 212 is pumped to the predetermined degree of vacuum, thewafer 1 for processing is conveyed to a convey chamber 213. Thereafter,the wafer 1 for processing is conveyed into a designated processingchamber, and is introduced so that the notch is oriented to a designateddirection inside the processing chamber. While the wafer 1 is conveyedinto the processing chamber 1 for example, pattern information over thewafer inputted to the control PC 205 is read. Information of the linedirection 9 of the measurement pattern at the irradiation point of theincident light is extracted from the pattern information having beenread, a notch direction 209, 210, 211 within the processing chamber, andinformation of the irradiation position the incident light formonitoring having been set beforehand, and a rotation angle 214, 215,216 of the polarization filter is rotated by a rotation mechanism 217,218, 219 respectively to an angle that makes the polarization direction10 of the incident light orthogonal namely 90 degrees to the directionof the line-and-space pattern. The relative positional relation of thenotch position 209, 210, 211 of the wafer, the irradiation position ofthe incident light, and the angle 214, 215, 216 of the polarizationfilter should be same for the processing chamber 1, 2, 3. Usually,because the direction of the line-and-space pattern formed over thewafer is parallel or orthogonal to the notch direction, such mechanismcapable of easily rotating the rotation direction of the polarizationfilter to 2 directions of 0° or 90° may be arranged. Also, theprocessing chamber 1, 2, 3 is not limited to the dry etching apparatus,and may be a deposition apparatus such as an atomic layer depositionapparatus.

Next, an example of the adjusting method for the irradiation position ofthe incident light and the position of the detection fiber of a casewhere the pattern area for monitoring the depo film thickness isapproximately several square millimeters or less and fine adjustment ofthe measuring position is necessary will be described. In the presentembodiment, the light source 102 and the optical fiber 106 for detectiondetecting the coherent light are installed on a movable stage whosestage position can be finely adjusted in the X-axis direction andY-direction. After the wafer for processing is conveyed to theprocessing chamber 1, the wafer is fixed to the stage of the processingchamber. First, the light emitted from the monitor light source 102 isirradiated to the measurement pattern, and the irradiation position isconfirmed by a measuring position aligning camera. As the positionaligning camera, a small sized camera such as a CCD camera and a CMOScamera can be used. The image of the measuring position captured by thecamera is displayed on the control PC 205. When the irradiation positiondeviates from the desired measurement pattern, a pattern layout drawingof the wafer information is displayed on the control PC 205, thepositional shifting is calculated by designating the position ofirradiation of the pattern on which the incident light irradiates atpresent and the position of the desired measurement pattern, and the XYstage can be adjusted to a desired position by the monitor control unit29.

In the configuration of the present embodiment, after adjusting themonitor light source to a desired position and irradiating the incidentlight 104 to the measurement pattern, the pattern with a desired shapecan be formed stably for a long time with excellent reproducibility bymonitoring the indicator of the depo film thickness and the indicator ofthe etching amount on a real-time basis using the method described inthe first embodiment.

Also, the present invention is not limited to the embodiments describedabove, and includes various modifications. For example, the embodimentsdescribed above were explained in detail for better understanding of thepresent invention, and are not necessarily limited to those includingall configurations explained. Also, a part of a configuration of anembodiment can be replaced with a configuration of another embodiment,and a configuration of an embodiment can be added with a configurationof another embodiment. Further, with respect to a part of aconfiguration of each embodiment, addition, deletion, and replacement ofother configurations are possible. Furthermore, with respect torespective configurations and functions as well as various kinds of thecontrol units and so on described above, although an example of workingout a program achieving some or all of them was explained, it is needlesto mention that some or all of them may be achieved by hardware by beingdesigned with an integrated circuit and so on for example. That is tosay, all or some of the functions of the control unit can be achieved byan ASIC (Application Specific Integrated Circuit), an FPGA (FieldProgrammable Gate Array), and so on for example instead of a program.

LIST OF REFERENCE SIGNS

-   1: Wafer-   2: Material to be etched-   3: Mask-   4: Non-etching layer-   5: Depo film-   6: Side wall-   7: Line-and-space pattern-   8: Polarization filter-   9: Line direction-   10: Polarization direction-   11: Notch-   20: Etching apparatus-   21, 201, 202, 203: Processing chamber-   22: Wafer stage-   23: Gas supply unit-   24: Depo process gas-   25: Etching process gas-   26: Detection unit-   27: Radio frequency power source-   28: Monitor unit-   29: Monitor control unit-   30: Bias power source-   31: Radio frequency application unit-   36: Apparatus control unit-   37: Gas control unit-   38: Exhaust system control unit-   39: Radio frequency control unit-   40: Bias control unit-   41: Storage unit-   42: Clock-   44: Radio frequency power-   45: Bias voltage-   46: Control signal-   47: Control line-   102: Light source-   103, 217, 218, 219: Rotation mechanism-   104: Incident light-   105: Coherent light-   106: Optical fiber-   107: Spectral apparatus-   108, 220: Control unit-   109: Calculation unit-   110: Database-   111: Fitting curve-   120: Hole pattern-   121: Side wall shape in the direction with a large pitch-   122: Side wall shape in the direction with a small pitch-   204: Wafer loader-   205: Control PC-   206: Rotation deck-   207: Convey robot-   208, 209, 210, 211: Notch position-   212: Load lock chamber-   213: Convey chamber-   214, 215, 216: Rotation angle of polarization filter-   221: Notch position adjustment stage

1. A plasma processing method for etching a film to be etched byrepeating a depositing process for forming a deposit layer over the filmto be etched and a removing process for removing a reaction product ofthe deposit layer and the film to be etched, comprising a monitoringprocess for monitoring a change amount of a film thickness of thedeposit layer using change of a coherent light that is obtained byirradiating a polarized light polarized to a predetermined angle withrespect to a mask pattern of the film to be etched and is reflected bythe mask pattern.
 2. The plasma processing method according to claim 1,wherein the predetermined angle is 90 degrees when the mask pattern is aline-and-space pattern.
 3. The plasma processing method according toclaim 1, wherein the monitoring process is for monitoring a changeamount of a film thickness of the deposit layer based on a differencebetween signal intensity of the coherent light of the removing processand signal intensity of the coherent light of the depositing process. 4.The plasma processing method according to claim 1, wherein themonitoring process is for monitoring a change amount of a film thicknessof the deposit layer based on an amplitude and a cycle length of afitting curve that is obtained using signal intensity of the coherentlight.
 5. The plasma processing method according to claim 2, wherein themonitoring process is for monitoring a change amount of a film thicknessof the deposit layer based on a difference between signal intensity ofthe coherent light of the removing process and signal intensity of thecoherent light of the depositing process.
 6. The plasma processingmethod according to claim 2, wherein the monitoring process is formonitoring a change amount of a film thickness of the deposit layerbased on an amplitude and a cycle length of a fitting curve that isobtained using signal intensity of the coherent light.
 7. The plasmaprocessing method according to claim 3, wherein the difference isstandardized by inclination of a fitting curve that is obtained usingsignal intensity of a coherent light of the removing process.
 8. Theplasma processing method according to claim 1, wherein, when the maskpattern is a hole pattern and a pitch in one direction in the holepattern is smaller than a pitch in another direction in the holepattern, the polarized light is polarized orthogonally to a pitch in theone direction, and the monitoring process is for monitoring a changeamount of a film thickness related to a deposit layer of a side wall ofthe hole pattern on a side of the other direction.
 9. The plasmaprocessing method according to claim 6, wherein, when the mask patternis a hole pattern and a pitch in one direction in the hole pattern issmaller than a pitch in the other direction in the hole pattern, thepolarized light is polarized orthogonally to a pitch in the onedirection, and the monitoring process is for monitoring a change amountof a film thickness related to a deposit layer of a side wall of thehole pattern on a side of the other direction.
 10. The plasma processingmethod according to claim 7, wherein, when the mask pattern is a holepattern and a pitch in one direction in the hole pattern is smaller thana pitch in another direction in the hole pattern, the polarized light ispolarized orthogonally to a pitch in the one direction, and themonitoring process is for monitoring a change amount of a film thicknessrelated to a deposit layer of a side wall of the hole pattern on a sideof the other direction.
 11. A plasma processing apparatus, comprising: aprocessing chamber where a sample is plasma-processed, a film to beetched being formed over the sample; a radio frequency power source thatsupplies radio frequency power for generating plasma; a sample deck onwhich the sample is mounted; a light source that irradiates light; apolarization filter that polarizes light irradiated from the lightsource to a predetermined angle with respect to a mask pattern of thefilm to be etched; a rotation mechanism that controls the rotation angleof the polarization filter; and a control unit where a change amount ofa film thickness of a deposit layer over the film to be etched isobtained using change of a coherent light that is obtained byirradiating the light polarized by the polarization filter whoserotation angle is controlled by the rotation mechanism and is reflectedby the mask pattern.
 12. The plasma processing apparatus according toclaim 11, wherein the rotation mechanism controls a rotation angle ofthe polarization filter so that the predetermined angle becomes 90degrees when the mask pattern is a line-and-space pattern.
 13. Theplasma processing apparatus according to claim 11, wherein, when plasmaprocessing for etching the film to be etched by repeating a depositingprocess for forming a deposit layer over the film to be etched and aremoving process for removing a reaction product of the deposit layerand the film to be etched is executed, the control unit obtains a changeamount of a film thickness of the deposit layer based on a differencebetween signal intensity of the coherent light of the removing processand signal intensity of the coherent light of the depositing process.14. The plasma processing apparatus according to claim 11, wherein, whenplasma processing for etching the film to be etched by repeating adepositing process for forming a deposit layer over the film to beetched and a removing process for removing a reaction product of thedeposit layer and the film to be etched is executed, the control unitobtains a change amount of a film thickness of the deposit layer basedon an amplitude and a cycle length of a fitting curve that is obtainedusing signal intensity of the coherent light.
 15. The plasma processingapparatus according to claim 13, wherein the difference is a valuestandardized by inclination of a fitting curve that is obtained usingsignal intensity of a coherent light of the removing process, when themask pattern is a hole pattern and a pitch in one direction in the holepattern is smaller than a pitch in another direction in the holepattern, the rotation mechanism controls a rotation angle of thepolarization filter so that the light is polarized orthogonally to apitch in the one direction, and the control unit obtains a change amountof a film thickness related to a deposit layer of a side wall of thehole pattern on a side of the other direction.